This is the result of marketing of the De Beers corporation, who ran large campaigns about "Diamonds are Forever" and how important an expensive engagement ring

This is the result of marketing of the De Beers corporation, who ran large campaigns about "Diamonds are Forever" and how important an expensive engagement ring was. That stuck quite well. https://en.m.wikipedia.org/wiki/De_Beers#Marketing https://en.m.wikipedia.org/wiki/De_Beers#Marketing